α-CH bond activation of coordinated Et2O via reaction of PR3 (R = Ph, Cy) with the cationic complex [C5Me5W(CO)3(OEt2)]+

Article abstract of DOI:10.1021/om950790z

Reaction of C₅Me₅W(CO)₃CH₃ (2) with [Et₂O)₂H]⁺BAr₄^- (Ar = 3,5-bis(trifluoromethyl)phenyl) produced the new cationic complex [C₅Me₅W(CO

Full text of DOI:10.1021/om950790z

2
Organometallics 1996, 15, 2-4
Communications
r-CH Bon d Activa tion of Coor d in a ted Et2O via Rea ction
of P R3 (R ) P h , Cy) w ith th e Ca tion ic Com p lex
[C5Me5W(CO)3(OEt2)]+
Chae S. Yi* and Dariusz Wo´dka
Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201-1881
Arnold L. Rheingold and Glenn P. A. Yap
Department of Chemistry, The University of Delaware, Newark, Delaware 19716
Received October 5, 1995X
Summary: Reaction of C5Me5W(CO)3CH3 (2) with
-
[Et2O)2H]+BAr4 (Ar ) 3,5-bis(trifluoromethyl)phenyl)
produced the new cationic complex [C5Me5W(CO)3-
(OEt2)]+BAr4- (1) in 82% isolated yield. The complex 1
readily undergoes ligand substitution reactions with
neutral donor ligands to give the complexes [C5Me5-
W(CO)3(L)]+BAr4- (L ) CH3CN (3), MeOH (4), H2O (5)).
In contrast, reaction of 1 with tertiary phosphines PR3
(R ) Ph, Cy) produced C5Me5W(CO)3H (6) and the new
phosphonium salts EtOCH(Me)PR3+BAr4- (R ) Ph (7),
Cy (8)), where the R-CH of Et2O has been selectively
displaced by phosphines.
tion of C5Me5W(CO)3CH3 (2)6 by strong acids HX (X )
Cl, I, CO2CF3) produced the complexes C5Me5W(CO)3X
and the liberation of methane.7 One possible mecha-
nism for this reaction involves protonation at the
tungsten center to form the cationic intermediate [C5-
Me5W(CO)3(H)CH3]+, followed by the reductive elimina-
tion of methane, and the subsequent coordination of X-
to form the complexes C5Me5W(CO)3X.
Direct stereoselective C-H bond activation of organic
ethers using transition-metal complexes is a potentially
useful method in organic synthesis.1 Although selective
oxidation of R-CH bonds of cyclic ethers has been
achieved using transition-metal-based oxidants such as
Cr2O3 and RuO4,2 the selective C-H bond activation of
the simple acyclic organic ethers remains as a difficult
problem. Normally an extremely reactive alkali-metal
species such as n-BuLi or KC4H9 is required to depro-
tonate Et2O.3 The relative ease of breaking the C-O
bond compared to the C-H bond also limits the practical
use of the C-H bond activation of acyclic ethers in
organic synthesis. Herein we report a selective R-CH
bond activation of coordinated Et2O from the reaction
of tertiary phosphines with the coordinated Et2O com-
In an attempt to directly observe the possible proto-
nated intermediate, an acid with a noncoordinating
anion, [(Et2O)2H]+BAr4- (Ar ) 3,5-bis(trifluoromethyl)-
phenyl),8 was employed. An Et2O (35 mL) solution of 2
(0.723 g, 1.72 mmol) was added dropwise to an Et2O
-
(25 mL) solution of [(Et2O)2H]+BAr4 (1.746 g, 1.72
mmol) at 0 °C. The initially yellow solution turned dark
red, and a red crystalline solid precipitated after 15 min
of additional stirring at 0 °C. The resulting precipitate
was filtered and recrystallized from ether/hexanes to
afford 1 as an analytically pure red crystalline solid
(82% yield). The complex 1 was completely character-
ized by spectroscopic and analytical methods.9 A set of
downfield-shifted Et2O peaks at δ 3.97 (q, J ) 7.2 Hz,
-
plex [C5Me5W(CO)3(OEt2)]+BAr4 (1).
1
OCH2) and 1.19 (t, J ) 7.2 Hz, OCH2CH3) in H NMR
Acid-induced elimination of alkanes has been an
effective method in preparing coordinatively unsatur-
ated cationic organometallic complexes.4 Following
Beck’s procedure,5 we recently found that the protona-
is consistent with a symmetric environment of the
(4) For recent selected examples, see: (a) Beck, W.; Su¨nkel, K. Chem.
Rev. 1988, 88, 1405. (b) J ordan, R. F.; Lapointe, R. E.; Bradley, P. K.;
Baenziger, N. Organometallics 1989, 8, 2892 and references therein.
(c) Brookhart, M.; Volpe, A. F., J r.; Lincoln, D. M.; Horva´th, I. T.;
Millar, J . M. J . Am. Chem. Soc. 1990, 112, 5634. (d) Caldarelli, J . L.;
Wagner, L. E.; White, P. S.; Templeton, J . L. J . Am. Chem. Soc. 1994,
116, 2878. (e) Hauptman, E.; Brookhart, M.; Fagan, P. J .; Calabrese,
J . C. Organometallics 1994, 13, 774. (f) Rix, F. C.; Brookhart, M. J .
Am. Chem. Soc. 1995, 117, 1137. (g) Vaughan, W. M.; Abboud, K. A.;
Boncella, J . M. Organometallics 1995, 14, 1567.
(5) (a) Su¨nkel, K.; Urban, G.; Beck, W. J . Organomet. Chem. 1985,
290, 231. (b) Appel, M.; Schloter, K.; Heidrich, J .; Beck, W. J .
Organomet. Chem. 1987, 322, 77. (c) Fischer, R. A.; Herrmann, W. A.
J . Organomet. Chem. 1987, 330, 377.
X Abstract published in Advance ACS Abstracts, December 15, 1995.
(1) For recent reviews, see: (a) Mitsunobu, O. In Comprehensive
Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: New York, 1991;
Vol. 6. (b) Cheshire, D. R. In Comprehensive Organic Synthesis; Trost,
B. M., Ed.; Pergamon Press: New York, 1991; Vol. 3. (c) J olly, P. W.
In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F.
G. A., Abel, E. W., Eds.; Pergamon Press: New York, 1982; Vol. 8. (d)
Masamune, S.; McCarthy, P. A. In Macrolide Antibiotics; Omura, S.,
Ed.; Academic Press: New York, 1984. (e) Recent Progress in the
Chemical Synthesis of Antibiotics; Lukas, G., Ohno, M., Eds.; Springer-
Verlag: Berlin, 1990.
(2) Godfrey, C. R. A. In Comprehensive Organic Synthesis; Trost,
B. M., Ed.; Pergamon Press: New York, 1991; Vol. 7.
(3) (a) March, J . Advanced Organic Chemistry, 4th ed.; Wiley: New
York, 1992. (b) Elschenbroich, C.; Salzer, A. Organometallics: A
Concise Introduction; VCH: New York, 1989.
(6) Mahmoud, K. A.; Rest, A. J .; Alt, H. G.; Eichner, M. E.; J ansen,
B. M. J . Chem. Soc., Dalton Trans. 1984, 175.
(7) Yi, C. S.; Wo´dka, D. Unpublished results.
(8) Brookhart, M.; Grant, B.; Volpe, A. F., J r. Organometallics 1992,
11, 3920.
0276-7333/96/2315-0002$12.00/0 © 1996 American Chemical Society

Communications
Organometallics, Vol. 15, No. 1, 1996
3
coordinated ether group. The complex 1 is remarkably
stable at room temperature under a nitrogen atmo-
sphere and can be handled briefly in air without
significant decomposition. Previously, syntheses of the
cycloepntadienyl analogue [C5H5(CO)3W(OEt2)]+X- (X
) PF6, AsF6) and related complexes [C5H5(CO)3M]+X-
(M ) Mo, W; X ) OSO2CF3, OSO2F, FBF3) have been
documented.4a,5
The structure of complex 1 was confirmed by X-ray
crystallography. The red prismatic single crystals of 1,
grown from layering hexanes on an Et2O solution, were
suitable for the X-ray crystal structure determination
(Figure 1).10 The molecular structure of 1 showed a
typical four-legged piano-stool arrangement. The bond
distance between W and O(1) of 2.197(7) Å is similar to
that in the previously reported cationic [CpW(CO)3-
(PriOH)]+ complex (W-O distance 2.186(9) Å),11 and no
unusual structural features on the coordinated Et2O
was observed.
F igu r e 1. Crystallographic structure of the cation of
[C5Me5W(CO)3(OEt2)]+BAr4- (1), drawn with 40% thermal
ellipsoids. Selected bond lengths (Å) and bond angles (deg):
W-cent, 1.988(8); W-O(1), 2.197(7); W-C(11), 1.978(11);
W-C(12), 2.006(11); W-C(13), 2.043(11); O(1)-W-cent,
108.0(2); C(11)-W-cent, 108.5(3); C(12)-W-cent, 122.4-
(3); C(13)-W-cent, 124.5(3).
As expected, the coordinated Et2O of 1 was readily
displaced by neutral donor ligands. For example, treat-
ment of 1 with CH3CN, MeOH, and H2O in Et2O at room
temperature led to the formation of the stable adducts
Me5(CO)3WH (6)13 and the new phosphonium salts
-
EtOCH(Me)PR3+BAr4 (R ) Ph (7), Cy (8)) in good to
excellent yields. The complexes 6-8 were separated
and completely characterized by spectroscopic meth-
ods.12 Diagnostic spectroscopic features for the phos-
phonium salts, the diastereotopic OCH2 groups (δ 3.87
(dq, J ) 9.0, 7.0 Hz, OCHHCH3), 3.49 (dq, J ) 9.0, 7.0
Hz, OCHHCH3) for 7) due to the asymmetric center on
the compound and the strong couplings between OCH-
CH3 hydrogens and the phosphorus atom (δ 5.01 (dq,
J HH ) 6.8 Hz, J PH ) 4.9 Hz, OCH(Me)PPh3) and 1.69
(dd, J PH ) 17.8, J HH ) 6.8 Hz, OCH(Me)PPh3) for 7),
-
[C5Me5(CO)3W(L)]+BAr4 (L ) CH3CN (3), MeOH (4),
H2O (5)) in good to excellent yields.12 In light of these
1
were seen by H NMR.14
Instead of displacing the coordinated Et2O, tertiary
phosphines apparently prefer to react at the R-carbon
of Et2O and transfer the R-hydrogen to the tungsten
center. Usually, the ligand substitution is the dominant
pathway for complexes with labile ligands such as Et2O,
CH3CN, and THF.15 The complex 1 also preferentially
undergoes ligand substitution reactions with sterically
undemanding and weakly nucleophilic neutral ligands
(CH3CN, MeOH, and H2O). When nucleophilic and
sterically demanding tertiary phosphines are employed,
however, an alternate pathway involving the R-CH bond
activation of the Et2O molecule was favored. The
electron-withdrawing effect of the cationic tungsten
center through the oxygen atom may also have facili-
tated the C-H bond activation. While transition-metal-
mediated C-H and C-O bond activation of cyclic ethers,
most notably THF, and R-CH bond activation of Et2O
results, we were surprised to find that complex 1
displayed a completely different reactivity pattern with
tertiary phosphines. Reaction of 1 with tertiary phos-
phines PR3 (R ) Ph, Cy) in Et2O at room temperature
cleanly produced a mixture of the previously known C5-
(9) Spectroscopic and analytical data for 1: 1H NMR (CD2Cl2, 300
MHz) δ 7.7-7.5 (m, Ar), 3.97 (q, J ) 7.2 Hz, CH2), 2.14 (s, C5Me5),
1.19 (t, J ) 7.2 Hz, CH2CH3); 13C NMR (CD2Cl2, 75 MHz) δ 229.1 (s,
J CW ) 80.7 Hz, 2CO’s), 225.4 (s, J CW ) 60.1 Hz, CO), 162.3 (1:1:1:1
quartet, J CB ) 49.2 Hz, Cipso), 135.3 (s, Cortho), 129.4 (q, J CF ) 31.5 Hz,
Cmeta), 125.1 (q, J CF ) 271.8 Hz, CF3), 118.0 (s, Cpara), 110.0 (s, C5Me5),
81.9 (s, CH2), 14.2 (s, CH2CH3), 11.0 (s, C5Me5); IR (CH2Cl2) νCO 2045
(s), 1968 (m), 1945 (s) cm-1; FAB MS m/e 477 (M+), 449 (M+ - CO),
403 (M+ - Et2O). Anal. Calcd for C49H37BF24O4W: C, 43.90; H, 2.79.
Found C, 43.87; H, 2.80. mp 122-124 °C.
(10) Crystallographic data for [C5Me5W(CO)3(OEt2)]{B[C6H3(CF3)2]4}
(1): C49H37BF24O4W, fw 1340.4, triclinic, P1h, a ) 13.169(7) Å, b )
13.282(5) Å, c ) 15.814(8) Å, R ) 72.63(4)°, â ) 88.02(4)°, γ ) 83.66-
(4)°, V ) 2624(2) Å3, Z ) 2, T ) 241 K. Of 9112 data collected
(maximum 2θ ) 49°, Mo KR), 8759 were unique. At convergence, R(F)
) 5.42% and R(wF) ) 6.34%. Several CF3 groups were rotationally
disordered and modeled with occupancy refinement.
(13) (a) Chi, Y.; Hsu, H.-Y.; Peng, S.-M.; Lee, G.-H. J . Chem. Soc.,
Chem. Commun. 1991, 1019. (b) Bruce, M. I.; Humphrey, M. G.;
Matisons, J . G.; Roy, S. K.; Swincer, A. G. Aust. J . Chem. 1984, 37,
1955. (c) Kazlauskas, R. J .; Wrighton, M. S. J . Am. Chem. Soc. 1982,
104, 6005. (d) Kubas, G. J .; Wasserman, H. J .; Ryan, R. R. Organo-
metallics 1985, 4, 2012.
(14) The J PH and J HH values of the phosphonium salts were
unambiguously assigned from the 1H{31P} NMR analysis.
(15) (a) Atwood, J . D. Inorganic and Organometallic Reaction
Mechanisms; Brooks/Cole: Monterey, CA, 1985; Chapter 4 and refer-
ences therein. (b) J ordan, R. F. Adv. Organomet. Chem. 1991, 32, 325.
(c) For common examples on the preparation of transition-metal
complexes with weakly coordinating ligands, see: Inorg. Synth. 1990,
28, 1.
(11) Song, J .-S.; Szalda, D. J .; Bullock, R. M.; Lawrie, C. J .; Rodkin,
M. A.; Norton, J . R. Angew. Chem., Int. Ed. Engl. 1992, 31, 1233.
(12) See the Supporting Information for detailed experimental
procedures and spectral data for complexes 3-5, 7, and 8.

4
Organometallics, Vol. 15, No. 1, 1996
Communications
in the presence of peroxides have been documented,16
to the best of our knowledge, our finding constitutes the
first example of the direct R-CH bond activation of
coordinated Et2O without any additional promoters.
We are currently investigating a detailed mechanism
of the reaction. In an attempt to extend the substitution
at the coordinated Et2O, complex 1 was reacted with
anionic nucleophiles. Reaction of 1 with the carbon
nucleophile KCH(CO2Me)2 led to the exclusive formation
of the dimeric tungsten species [C5Me5W(CO)3]2 (9)17
and the protonated CH2(CO2Me)2, while the reaction
with LiBEt3D (99% D, 1.0 M in THF) gave predomi-
nantly the tungsten hydride 6 with <10% of deuterium
on the hydride as determined by NMR.18 The formation
of dimeric 9 may have resulted from the deprotonation
reaction of the initially generated tungsten hydride
complex 6 to produce anionic C5Me5W(CO)3-, followed
by its coupling reaction with the unreacted cationic 1.
The formation of hydride complex 6 (and not deuteride
complex) from the reaction with LiBEt3D is also con-
sistent with the migration of the R-hydrogen to the
tungsten center. A similar reaction of 1 with the organic
base Et3N resulted in the formation of the dimer 9 and
-
Et3NH+BAr4
.
In summary, selective substitution on the R-carbon
of the coordinated Et2O from the reaction with tertiary
phosphines has been described. We have demonstrated
that the selective R-CH bond activation of normally
unreactive acyclic Et2O can be achieved using the
electrophilic organometallic complex 1. Our method is
potentially useful in the selective activation of other
acyclic ethers. Studies directed on the scope and the
mechanism of the reaction are currently underway.
Ack n ow led gm en t. Financial support from the Mar-
quette University Committee-on-Research is gratefully
acknowledged. We thank Drs. William A. Donaldson
and Maciej K. Tasz for helpful discussions.
(16) (a) Boutry, O.; Gutie´rrez, E.; Monge, A.; Nicasio, M. C.; Pe´rez,
P. J .; Carmona, E. J . Am. Chem. Soc. 1992, 114, 7288. (b) Li, Z-W.;
Taube, H. J . Am. Chem. Soc. 1994, 116, 11584. (c) Breen, T. L.;
Stephan, D. W. Inorg. Chem. 1992, 31, 4019. (d) Lehmkuhl, H.;
Schwickardi, R.; Kru¨ger, C.; Raabe, G. Z. Anorg. Allg. Chem. 1990,
581, 41. (e) Werner, H.; Weber, B.; Nu¨rnberg, O.; Wolf, J . Angew.
Chem., Int. Ed. Engl. 1992, 31, 1025. (f) Hay-Motherwell, R. S.;
Hussain-Bates, B.; Hursthouse, M. B.; Mann, B. E. J . Chem. Soc.,
Dalton Trans. 1993, 3219.
(17) (a) King, R. B.; Iqbal, M. Z.; King, A. D., J r. J . Organomet.
Chem. 1979, 171, 53. (b) Rheingold, A. L.; Harper, J . R. Acta
Crystallogr. 1991, C47, 184. (c) Bougeard, P.; Peng, S.; Mlekuz, M.;
McGlinchey, M. J . J . Organomet. Chem. 1985, 296, 383.
Su p p or tin g In for m a tion Ava ila ble: Text giving spec-
troscopic data for complexes 3-5, 7, and 8 and tables giving
the structure determination summary, positional and thermal
parameters, bond distances, and bond angles for 1 (14 pages).
This material is contained in many libraries on microfiche,
immediately follows this article in the microfilm version of the
journal, can be ordered from the ACS, and can be downloaded
from the Internet. See current masthead page for ordering
information and Internet access instructions.
(18) We also observed the formation of a small amount (∼5%) of
the dimer 9 in the reaction mixture.
OM950790Z